In ink-jet printing methods, droplets of ink are directly projected onto a recording medium from very fine nozzles and allowed to adhere to the recording medium, to form images or characters. The ink-jet printing methods have become rapidly spread because of various advantages such as easiness of full coloration, low cost, capability of using a plain paper as the recording medium, non-contact with printed images or characters, etc.
In recent years, in order to impart a good weathering resistance and a good water resistance to printed matters, an ink containing a pigment as a colorant has been extensively used.
For example, JP 2001-329199A discloses an aqueous ink composition that is capable of exhibiting excellent water resistance, rub fastness and highlighter fastness, and includes an aqueous medium, polymer particles A obtained by incorporating a pigment into a water-insoluble polymer and/or a self-dispersible pigment, and polymer particles B, in which methoxypolyethylene glycol (meth)acrylate is used as a monomer for the polymer.
JP 2006-282989A discloses a water-based ink for ink-jet printing which is capable of not only satisfying a high optical density but also exhibiting an excellent highlighter fastness, and includes a water dispersion containing colorant-containing polymer particles (A-1), polymer particles (B) and a water-insoluble organic compound.
JP 2010-84116A discloses an ink for ink-jet printing which is excellent in quality of images printed on a plain paper, suitability for high-speed printing, etc., and includes a water dispersion of pigment-containing water-insoluble vinyl polymer particles, a water-soluble organic solvent and water, in which a residue of the ink which is obtained by allowing the ink to stand until substantially no further change in mass of the ink occurs has a viscosity not more than a specific value, and an ink preparation whose pH value is controlled to 7 has a viscosity of not less than 500 mPa·s.
On the other hand, there is an increasing demand for printed matters printed on recording media for commercial printing use including not only high-absorptive recording media such as the aforementioned conventional plain paper and a so-called copy paper, but also a low-liquid absorbing coated paper such as an offset coated paper or a non-liquid absorbing resin film such as a polyvinyl chloride resin film, a polypropylene resin film and a polyester resin film.
It is known that when images or characters are printed on the low-liquid absorbing or non-liquid absorbing recording media by the ink-jet printing methods, there tend to occur problems such as slow absorption of liquid components, prolonged drying time owing to poor absorption, and deterioration in rub fastness in an early stage of printing.
Also, if the amount of the solvent in the ink is reduced to shorten the drying time, there is such a tendency that the ink fails to spread over the recording medium to cause formation of spots in images and deterioration in ejection property of the ink. To solve these problems, the ink-jet printing method using a recording medium having an ink absorbing layer has been proposed.
For example, JP 2005-36202A discloses an ink-jet printing method using a water-based ink containing colorant-containing water-insoluble vinyl polymer particles and a void-type glossy medium in which the water-insoluble vinyl polymer is produced from a polyoxyethylene chain-containing (meth)acrylate monomer, a salt-forming group-containing monomer and a hydrophobic monomer.